Encapsulated miniature hard disc drive

ABSTRACT

A miniature hard disc drive has a metal base plate, an actuator assembly wherein the actuator assembly comprises a plurality of bearings, a shaft, and a housing; a spindle motor assembly comprising a stator with conductors, a shaft, a plurality of bearings, and a rotor; and a monolithic body of phase change material unitizing the actuator assembly housing and stator to the base plate. Methods of developing and constructing the hard disc drive are also disclosed.

REFERENCE TO RELATED APPLICATION

The present application is a continuation of application Ser. No.11/225,233, filed Sep. 12, 2005, which is a divisional of applicationSer. No. 10/001,692, filed Oct. 25, 2001, U.S. Pat. No. 6,941,640, allof which are hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates generally to a hard disc drive. It relatesparticularly to a miniature hard disc drive that uses a high speedspindle motor assembly, an actuator assembly and to the construction andarrangement of the spindle motor assembly and actuator assembly to alignand retain the respective component parts of the assemblies, as well asmotor and other component assemblies used in the miniature hard discdrive, and methods of manufacturing hard disc drives.

BACKGROUND OF THE INVENTION

Computers commonly use disc drives for memory storage purposes. Discdrives include a stack of one or more magnetic discs that rotate and areaccessed using a head or read-write transducer. Miniature hard discdrives are smaller than other hard disc drives and are used in hand-heldelectronic devices and portable electronic devices such as cellularphones, hand-held personal computers, digital cameras and personaldigital assistants (PDA's). Typically, a high-speed motor such as aspindle motor is used to rotate the discs. An example of a miniaturehard disc drive is International Business Machines' (IBM) Microdrive™.

An example of a conventional spindle motor 1 used in a hard disc driveis shown in FIG. 1. The motor 1 includes a base 2 which is usually madefrom die cast aluminum, a stator 4, a shaft 6, bearings 7 and a discsupport member 8, also referred to as a hub. A magnet 3 and flux returnring 5 are attached to the disc support member 8. The stator 4 isseparated from the base 2 using an insulator (not shown) and attached tothe base 2 using a glue. Distinct structures are formed in the base 2and the disc support member 8 to accommodate the bearings 7. One end ofthe shaft 6 is inserted into the bearing 7 positioned in the base 2 andthe other end of the shaft 6 is placed in the bearing 7 located in thehub 8. A separate electrical connector 9 may also be inserted into thebase 2.

Each of these parts must be fixed at predefined tolerances with respectto one another. Accuracy in these tolerances can significantly enhancemotor performance.

In operation, the disc stack is placed upon the hub. The stator windingsare selectively energized and interact with the permanent magnet tocause a defined rotation of the hub. As hub 8 rotates, the head (notshown) engages in reading or writing activities based upon instructionsfrom the CPU in the computer.

Manufacturers of disc drives are constantly seeking to improve the speedwith which data can be accessed. To an extent, this speed depends uponthe speed of the spindle motor, as existing magneto-resistive headtechnology is capable of accessing data at a rate greater than the speedoffered by the highest speed spindle motor currently in production. Thespeed of the spindle motor is dependent upon the dimensional consistencyor tolerances between the various components of the motor. Greaterdimensional consistency between components leads to a smaller gapbetween the stator 4 and the magnet 3, producing more force, whichprovides more torque and enables faster acceleration and higherrotational speeds. One drawback of conventional spindle motors is that anumber of separate parts are required to fix motor components to oneanother. This can lead to stack up tolerances which reduce the overalldimensional consistency between the components. Stack up tolerancesrefers to the sum of the variation of all the tolerances of all theparts, as well as the overall tolerance that relates to the alignment ofthe parts relative to one another.

An important characteristic of a hard drive is the amount of informationthat can be stored on a disc. One method to store more information on adisc is to place data tracks more closely together. Presently thisspacing between portions of information is limited due to vibrationsoccurring during the operation of the motor. These vibrations can becaused when the stator windings are energized, which results invibrations of a particular frequency. These vibrations also occur fromharmonic oscillations in the hub and discs during rotation, causedprimarily by non-uniform size media discs.

An important factor in motor design is the lowering of the operatingtemperature of the motor. Increased motor temperature affects theelectrical efficiency of the motor and bearing life. As temperatureincreases, resistive loses in wire increase, thereby reducing totalmotor power. Furthermore, the Arhennius equation predicts that thefailure rate of an electrical device is exponentially related to itsoperating temperature. The frictional heat generated by bearingsincreases with speed. Also, as bearings get hot they expand, and thebearing cages get stressed and may deflect, causing non-uniform rotationand the resultant further heat increase, non-uniform rotation requiringgreater spacing in data tracks, and reduced bearing life. One drawbackwith existing motor designs is their limited effective dissipation ofthe heat, and difficulty in incorporating heat sinks to aid in heatdissipation. In addition, in current motors the operating temperaturesgenerally increase as the size of the motor is decreased.

Manufacturers have established strict requirements on the outgassing ofmaterials that are used inside a hard disc drive. These requirements areintended to reduce the emission of materials onto the magnetic media orheads during the operation of the drive. Of primary concern are gluesused to attach components together, varnish used to insulate wire, andepoxy used to protect steel laminations from oxidation.

In addition to such outgassed materials, airborne particulate in a drivemay lead to head damage. Also, airborne particulates in the disc drivecould interfere with signal transfer between the read/write head and themedia. To reduce the effects of potential airborne particulate, harddrives are manufactured to exacting clean room standards and air filtersare installed inside of the drive to reduce the contamination levelsduring operation.

With the rapidly expanding development of personal computers into thefield of first what was termed portable, then lap-top, notebook and nowhand held size computers and digital cameras, there has been atremendous demand for smaller disc drives with increased performance forsuch small computers. Especially important to manufacturers, is theability to reduce the height of the disc drive so that the size of thecasing for the computer could be minimized. It is an objective of thepresent invention to provide a compact hard disc drive system that iscompatible with notebook and hand held computer applications, and can becompatible with devices using Type I and Type II Flash memory devices.

Another objective of the invention is to provide a compact hard discdrive system that has lower vibration and greater structural integrityto provide increased data storage capability and increased speed.

Another example of a spindle motor that can be used in a hard drive isshown in U.S. Pat. No. 5,694,268 (Dunfield et al.) (incorporated hereinby reference). Referring to FIGS. 7 and 8 of this patent, a stator 200of the spindle motor is encapsulated with an overmold 209. Theovermolded stator contains openings through which mounting pins 242 maybe inserted for attaching the stator 200 to a base. U.S. Pat. No.5,672,972 (Viskochil) (incorporated herein by reference) also disclosesa spindle motor having an overmolded stator. One drawback with theovermold used in these patents is that it has a different coefficient oflinear thermal expansion (“CLTE”) than the corresponding metal parts towhich it is attached. Another drawback with the overmold is that it isnot very effective at dissipating heat. Further, the overmolds shown inthese patents are not effective in dampening some vibrations generatedby energizing the stator windings.

U.S. Pat. No. 5,806,169 (Trago) (incorporated herein by reference)discloses a method of fabricating an injection molded motor assembly.However, the motor disclosed in Trago is a step motor, not a high-speedspindle motor, and would not be used in applications such as hard discdrives. Furthermore, none of these prior art embodiments integrate thebase of the hard disc drive, thereby eliminating the cost of the base.Thus, a need exists for an improved miniature hard disc drive that issmall and lightweight yet overcomes the aforementioned problems.

BRIEF SUMMARY OF THE INVENTION

A miniature hard disc drive has been invented which overcomes many ofthe foregoing problems. In addition, unique stator assemblies and othercomponents of a high-speed motor have been invented, as well as methodsof manufacturing hard disc drives. In one aspect, the invention is ahard disc drive having an actuator assembly that includes an actuatorassembly housing; a spindle motor assembly having a stator withconductors, a rotor, a shaft, and a plurality of bearings; a base plate;and a monolithic body of phase change material substantiallyencapsulating said actuator assembly housing and said stator to the baseplate.

In another aspect, the invention is a miniature hard disc drive having ametal base plate; an actuator assembly wherein the actuator assembly hasa plurality of bearings, a shaft, and a housing; a spindle motorassembly having a stator with conductors, a shaft, a plurality ofbearings, and a rotor; and a monolithic body of phase change materialunitizing said actuator assembly housing stator to the base plate.

In yet another aspect, the invention is a method for making a miniaturehard disk drive including the steps of providing a stator having aplurality of poles with wire windings around said poles; providing anactuator assembly housing; providing a base plate; substantiallyencapsulating the stator, the actuator assembly housing and the baseplate with a phase change material so as to form a unitized body; andforming a miniature hard disc drive from said unitized body.

The invention provides the foregoing and other features, and theadvantages of the invention will become further apparent from thefollowing detailed description of the presently preferred embodiments,read in conjunction with the accompanying drawings. The detaileddescription and drawings are merely illustrative of the invention and donot limit the scope of the invention, which is defined by the appendedclaims and equivalents thereof.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is an exploded, partial cross-sectional and perspective view of aconventional high-speed motor.

FIG. 2 is a top view of a hard disc drive of the present invention withthe cover, actuator and read-write head removed, and showing theremaining components encapsulated in the monolithic body with dashedlines.

FIG. 3 is a cross-sectional view of the hard disc drive of FIG. 2 withits cover on, but without the actuator and read-write head, from avertical cross-sectional view sectioned along line 3-3 of FIG. 2.

FIG. 4 is a top view of a metal strip after being through the injectionmolding process.

FIG. 5 is a perspective view of a metal strip with a base plate made byan injection molding process of the present invention.

FIG. 6 is a perspective view of a metal strip with a base plate andcover made by an injection molding process of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The miniature hard disc drive 10 of the present invention is shown froma top view (with the cover shell removed) in FIG. 2 and in FIG. 3 from avertical sectional view sectioned along a line through the spindle motorand actuator assembly axes of rotation. In each of the figures likecomponents are designated by like reference numerals.

Referring to FIG. 3, the major elements of the miniature hard disc drivesystem 10 of the present invention are shown, including hard disc 100,spindle motor assembly 200, and an actuator assembly 300. Thesecomponents are attached to a base portion 108 of a housing. The baseplate 108 is preferably made of stamped steel. A shell portion forms acover 111, and in conjunction with the base portion 108, encloses theaforementioned disc drive components.

The hard disc 100 preferably has a diameter of about 27 millimeters. Thedisc 100 has a centrally located aperture through which a hub 102extends. Each disc 100 is preferably constructed from glass, aluminum,or canestite having a thickness of about 0.38 millimeters and is coatedwith a magnetic material. Once formatted each disc is capable of havingmore than 2000 tracks per inch of accessible storage space. This densityof tracks enables a miniature disc drive to store more than 20 MB ofdata in a single disc system. Discs meeting these requirements areavailable from Yamaha, Fuji Corporation and Hitachi Corporation, all ofJapan.

The disc drive explained herein utilizes one or more magnetic coateddiscs 100; however, the disc drive may utilize various numbers and typesof discs. For example, optical discs and associated laser technologybased read/write heads could be used and the concepts and principlesembodied in this invention would be fulfilled.

The means for rotatably supporting the hard disc 100 is a hub 102 whichis an integral part of the rotor 210 of a spindle motor assembly 200. Inthe preferred embodiment of the present invention and as depicted inFIG. 3, one concentrically aligned disc 100 is positioned on the hub102. The disc drive depicted is a single disc system; however, toincrease storage capability, multi-disc systems are foreseeable.

As depicted in FIG. 3, the means for rotating the hard disc 100 ispreferably a spindle motor assembly 200 having an integral hub 102. Thespindle motor 200 includes a stator 204, a rotor 210, a shaft 206, andbearing supports 208. The stator 204 has a plurality of poles 207 withwire windings 205. Preferably each pole 207 has about 50 turns of copperwire 205 with an American wire gauge number of 38. The wire windings 205serve as conductors and induce or otherwise create a plurality ofmagnetic fields when electrical current is conducted through theconductors. In this embodiment, a magnetic field is induced in each ofthe poles 207.

In the present embodiment, the integral hub 102 is fixedly mounted to ashaft 206 forming the axis of rotation 202 of the motor 200. The shaft206 is mounted to the base plate 108 using pins (not shown) or otherconventional mounting means. Bearing supports 208 are journalled aboutthe shaft 206 and support a rotor 210 comprised of the hub 102 and apermanent magnet 214 positioned on a outer surface of the hub 102 facingthe stator 204. The interaction of a magnetic field generated by thestator 204 with the rotor permanent magnets 214 propels the rotor 210 tospin. The rotor 210, having the hub 102 as an integral component,rotates the hard disc 100. In the preferred embodiment shown in FIG. 3,there is also a base 215 that houses bearing supports 208 and shaft 206.The base 215 is not essential to practice the invention and can beremoved, and instead the hub 102 can be used to house the bearingsupports 208 and shaft 206.

The actuator assembly 300 has a voice coil motor (not shown) that drivesan actuator arm (not shown) to pivot and swing back and forth over thedisc surface 100 to read and write data. The actuator assembly arm isattached to a shaft 306 or actuator pivot at one end. The other end ofthe actuator arm has a head that reads and writes data. The shaft 306 ismounted to the base plate 108 through pins or other conventionalmounting means. Bearing supports 308 are journalled about the shaft 306.The bearing supports 308 and shaft 306 are housed in a metal housing310. The metal housing 310 is preferably made of steel.

Referring to FIGS. 2 and 3, the stator 204 of the spindle motor assembly200 and the housing 310 of the actuator assembly 300 are unitized withthe base plate 108 by encapsulating them with a top surface of baseplate 108. Conventionally, the spindle motor assembly and actuatorassembly are mounted to the base using conventional mounting featuressuch as connecting pins or glue. In the present embodiment, the stator204 and the housing 310 of the actuator assembly 300 and a top surfaceof the base plate 108 are encapsulated with a phase change material toform a unitized, preferably monolithic, body 250. The phase changematerial used to make the body 250 is preferably a thermally conductivebut non-electrically conductive plastic. In addition, the plasticpreferably includes ceramic filler particles of either boron nitride orpreferably aluminum nitride. The coefficient of linear thermal expansion(“CLTE”) of the plastic is preferably between the CLTE of steel and theCLTE of aluminum over the operating temperature range of the hard discdrive. A preferred form of plastic is polyphenyl sulfide (PPS) soldunder the trade name “Konduit” by LNP Engineering Plastics. GradeOTF-212-11 is particularly preferred. Examples of other suitablethermoplastic resins include, but are not limited to, thermoplasticresins such as 6,6-polyamide, 6-polyamide, 4,6 polyamide,12,12-polyamide, and polyamides containing aromatic monomers,polybutylene terephthalate, aromatic polyesters, liquid crystalpolymers, polycyclohexane dimethylol terephthalate, copolyetheresters,polyphenylene sulfide, polyacylics, polypropylene, polyethylene,polyacetals, polymethylpentene, polyetherimides, polycarbonate,polysulfone, polyethersulfone, polyphenyloxide, polystyrene, styrenecopolymer, mixterus and graft copolymers of styrene and rubber, andglass reinforced or impact modified versions of such resins. Blends ofthese resins such as polyphenylene oxide and polyamide blends, andpolycarbonate and polybutylene terephthalate, may also be used in theinvention.

As illustrated in FIGS. 2 and 3, the body 250 encapsulates a substantialarea of a top surface of the base plate 108, stator 204, and theexternal surface of actuator assembly housing 310. After encapsulation,the actuator assembly housing 310 and the stator 204 are unitized withbase plate 108. The body 250 extends over the top surface of stator 204and preferably terminates around the inner edge 211 of stator 204. Theinner side surface 212 of stator 204 is preferably left un-encapsulatedto obtain the smallest distance between the conductors and permanentmagnet 214. The inner side surface 212 may be encapsulated with a thinlayer of phase change material without deviating from the scope of thepresent invention. The thickness of the body 250 may vary but ispreferably at least about 0.2 millimeters. The critical thicknessrequired is that the body 250 must be thick enough so that it extendsover the top surface of stator 204. Preferably, for greater structuralintegrity the body 250 may be thicker around the edge of the base plate108.

The hard drive shown in FIGS. 2 and 3 is made in part using anencapsulation technique. This encapsulation technique involves thefollowing steps, and uses an injection mold. First, a mold isconstructed to produce a part with desired geometry. The mold has twohalves or cavities. In a preferred embodiment, the base plates arestamped into a continuous strip of metal which is fed through the mold.As shown in FIG. 4, the strip 130 creates multiple plates 108. Inalternative embodiments, the base plates 108 can be placed side by sidefor multicavity molding, or as is shown in FIG. 6 the cover can befabricated on the same strip of metal.

A preferred embodiment has the cover and base plate fabricated side byside during molding, as shown in FIG. 6. In this process a metal striphaving both a base plate and a cover is placed in a two cavity mold. Amonolithic body of phase change material is then injected onto the baseplate and onto the cover to form lips, grooves, and other body features.After the strip is removed from the molding machine, and after the otherinternal components have been added to the drive, the cover is attachedto the base plate using processes well known in the art, such as heatstaking, sonic welding or gluing. The cover may be located on the baseusing details formed in the monolithic body of phase change material,such as the studs and holes shown in FIGS. 5 & 6.

During encapsulation the base plate is placed in one half of the moldand is held in place by protrusions from the mold plate which extendthrough an aperture 135 in the base plate. The base plate 108, actuatorassembly housing 310 and the stator 204 are aligned in position and thetwo halves are closed. Plastic is injected at a pre-determined pressurearound the stator 204, actuator assembly housing 310 and base plate 108so as to unitize those respective parts of the hard disc drive and formthe body 250 shaped as shown in FIGS. 2 and 3. Likewise plastic can bemolded around a circuit board or metal plate to form the HDD cover.After the pressure inside the mold reaches the pre-determined set pointpressure, the phase change material is allowed to cool and solidify.This process is repeated sequentially for the rest of the base plates108 if a metal strip 130 is employed.

Once the encapsulation process is complete, the other components of theactuator assembly and spindle motor assembly are assembled throughconventional methods. In an alternative embodiment, it is alsocontemplated that the entire spindle motor assembly may be encapsulatedwith the actuator assembly being formed later or vice versa. It is alsocontemplated that the actuator assembly and the spindle motor assemblycan be encapsulated with the base plate. Other variations are alsocontemplated wherein at least one or more of the non-moving parts of thehard disc drive are encapsulated with the base plate. In yet anotherembodiment, it is contemplated that a base plate is injection moldedwith a layer of phase change material to form various body features suchas lips, flanges and grooves. These methods are described more fully inprovisional U.S. patent application Ser. No. 60/171,817, filed Dec. 21,1999, incorporated herein by reference.

In another preferred embodiment, the metal strip 130 has apertures 135which are compatible with machines that are used for other manufacturingsteps, so that the strip 130 acts as a carrier which can be used invarious manufacturing steps. By acting as a carrier, it is meant thatthe metal strip 130 and the apertures 135 are configured in a mannersuch that the metal strip can be handled by machines, other than aninjection molding machine, that are used in the manufacturing process ofa hard disc drive. As a result, using the strip 130 with apertures 135offers an easy way to manipulate small parts. Furthermore, it offers away to ship the strips 130 to a customer for further assemblyoperations.

As illustrated in FIG. 6, the metal strip 130 having a base plate 108and cover 111 may be fed continuously into an injection molding machinewhich would perform the injection molding step on each base plate andcover. The injection molding machine encapsulates hard disc drivecomponents to the base plate and forms body features on the cover with amonolithic body of phase change material. The injection molding machinepreferably performs these steps simultaneously, but it is also possibleto perform them sequentially. One of ordinary skill in the art willappreciate that it is also possible to have an injection molding machinewith multiple cavities so that several metal strips may be fed into theinjection molding machine, thereby further increasing the efficiency ofthe process. After removing the metal strip from the mold, the cover maybe separated from the strip or folded over and fixedly attached to thebase plate.

Following the encapsulation technique in accordance with one embodimentof the invention a hard disc drive with a thickness between about twomillimeters to about six millimeters may be manufactured. Preferably, inone embodiment, the disc drive would be about 3.3 millimeters thick,which corresponds with a miniature disc drive used to replace Type Iflash memory devices. In another preferred embodiment, a thicker discdrive with a thickness of about 5 millimeters may also be manufacturedthat can be used to replace Type II flash memory devices.

Additionally, to reduce height and improve manufacturability, in onealternative embodiment, the cover 111 of the hard drive can be a printedcircuit board. Using a circuit board as a cover obviates the necessityof having a separate cover. It is also contemplated that plastic may beinjection molded around the edges of the cover so that the edges of thecover and the base plate 108 are made from the same material. In thismanner the cover may also be fixed to the base plate by methods wellknown in the art, such as heat staking, sonic welding or gluing.

The present invention is also directed to a method of developing aminiature hard disc drive 10. In an exemplary embodiment, the hard discdrive includes a stator having conductors and the stator issubstantially encapsulated in a body of phase change material. It hasbeen found that using this basic design concept, high-speed motors canbe developed and quickly optimized to meet various applications. Thereare several basic design parameters that can be varied when developing amotor according to the present invention: a) the composition (and thuscharacteristics) of the phase change material; b) the configuration ofthe body of phase change material; c) the magnetic design of the motor(the windings, core shape, etc.); d) the shape, size and configurationof the hub (and any discs used thereon when the motor is for a harddrive); and e) the shape, size and configuration of the actuatorassembly.

In a first embodiment, where a miniature hard disc drive is developed,the method includes the following steps: a) providing an actuatorassembly housing, a base plate, and a stator having multiple conductorsthat create a plurality of magnetic fields when electrical current isconducted through the conductors, the stator and actuator assemblyhousing being unitized with a base plate by substantially encapsulatingwith a body of first phase change material; b) mounting the disc andother components of the miniature hard disc drive through conventionalmeans; c) energizing the actuator assembly and the spindle motorassembly in a manner that generates vibrations, and measuring thefrequency of the vibrations; d) designing a second phase change materialthat dampens the vibrations generated by energizing the stator in stepc); and e) repeating steps a)-c), substituting the second phase changematerial for the first phase change material. At least one of the flexmodulus, elongation and surface hardness properties of the phase changematerial will be adjusted between the first and second phase changematerials to optimize vibration dampening. The phase change material ispreferably a thermoplastic. The advantages of this method of developinga hard disc drive is that the above-identified properties of the plasticmay be adjusted to meet the vibration dampening needs of a variety ofdifferent motor types and configurations. The reduced vibration willimprove motor performance and can reduce audible noise generation.

It is also possible to change the configuration of the body so that itwill result in reduced harmonic oscillations and thus vibrations. Inthis embodiment, the method includes the steps of and a) providing anactuator assembly housing, a base plate, and a stator having multipleconductors that create a plurality of magnetic fields when electricalcurrent is conducted through the conductors, the stator and actuatorassembly housing being unitized with a base plate by substantiallyencapsulating with a body of first phase change material; b) mountingthe disc and other components of the miniature hard disc drive throughconventional means; c) energizing the actuator assembly and the spindlemotor assembly in a manner that generates vibrations, and measuring thefrequency of the vibrations; d) reconfiguring the shape of the phasechange material to a second configuration and repeating steps a)-c),substituting the phase change material having the second configurationfor the phase change material having the first configuration. In thisembodiment, the configuration of the body of phase change material isadjusted to optimize vibration dampening. Of course, other dimensions ofbody components can also be used. In this aspect of the invention,reconfiguring the shape of the phase change material would also includeadding such elements as a flange, grooves, etc., or even adopting arelatively different overall shape.

The present invention is also directed to an alternative method ofdeveloping a miniature hard disc drive. Like the other methods, thismethod also involves a high-speed motor that includes a body that iscomprised of a phase change material that unitizes some components of ahard disc drive. The high-speed motor includes one or more, andgenerally a plurality of solid parts to be used in the motor either nearor within the body, such as bearings and inserts. In addition, there aresolid parts that are near the body, such as a disc support member and ahard disc drive base. The method of developing the high-speed motorcomprises designing a phase change material to have a coefficient oflinear thermal expansion such that the phase change material contractsand expands at approximately the same rate as the one or more solidparts. For example, the preferred phase change material should have aCLTE of between 70% and 130% of the CLTE of the core of the stator. Thephase change material should have a CLTE that is intermediate themaximum and minimum CLTE of the solid parts where the body is in contactwith different materials. Also, the CLTE's of the body and solid part(s)should match throughout the temperature range of the motor during itsoperation. An advantage of this method is that a more accurate tolerancemay be achieved between the body and the solid parts because the CLTE ofthe body matches the CLTE of the solid parts more closely.

Most often the solid parts will be metal, and most frequently steel,copper and aluminum. The solid parts could also include ceramics. Inalmost all motors there will be metal bearings. Thus a common element ofthis aspect of the invention is developing a motor by designing thephase change material to have a CLTE approximately the same as that ofthe metal used to make the base plate 108.

Most thermoplastic materials have a relatively high CLTE. Somethermoplastic materials may have a CLTE at low temperatures that aresimilar to the CLTE of metal. However, at higher temperatures the CLTEdoes not match that of the metal. A preferred thermoplastic materialwill have a CLTE of less than 2×10⁻⁵ in/in° F., more preferably lessthan 1.5×10⁻⁵ in/in° F., throughout the expected operating temperatureof the motor, and preferably throughout the range of 0° F. to 250° F.Most preferably, the CLTE will be between about 0.8×10⁻⁵ in/in° F. andabout 1.2×10⁻⁵ in/in° F. throughout the range of 0° F. to 250° F. Whenthe measured CLTE of a material depends on the direction of measurement,thickness of the sample, or conditions of molding, the relevant CLTE forpurposes of defining the present invention is the CLTE of anencapsulated component in the direction in which the CLTE is lowest.Preferably, the CLTE in other directions is not more than 4 times thelowest value. The CLTE values are measured by a standard ASTM testmethod where the phase change material has the shape and form of themonolithic body that is overmolded on a component.

The CLTE of common solid parts used in a motor are as follows: 23° C.250° F. Steel 0.5 0.8 (×10⁻⁵ in/in/° F.) Aluminum 0.8 1.4 Ceramic 0.30.4

Of course, if the motor is designed with two or more different solids,such as steel and aluminum components, the CLTE of the phase changematerial would preferably be one that was intermediate, the maximum CLTEand the minimum CLTE of the different solids, such as 0.65 in/in/° F. atroom temperature and 1.1×10⁻⁵ in/in/° F. at 250° F.

One preferred thermoplastic material, Konduit OTF-212-11, was made intoa thermoplastic body and tested for its coefficient of linear thermalexpansion by a standard ASTM test method. It was found to have a CLTE inthe range of −30 to 30° C. of 1.09×10⁻⁵ in/in/° F. in the X directionand 1.26×10⁻⁵ in/in/° F. in both the Y and Z directions, and a CLTE inthe range of 100 to 240° C. of 1.28×10⁻⁵ in/in/° F. in the X directionand 3.16×10⁻⁵ in/in/° F. in both the Y and Z directions. (Hence, therelevant CLTEs for purposes of defining the invention are 1.09×10⁻⁵in/in/° F. and 1.28×10⁻⁵ in/in/° F.) Another similar material, KonduitPDX-0-988, was found to have a CLTE in the range of −30 to 30° C. of1.1×10⁻⁵ in/in/° F. in the X direction and 1.46×10⁻⁵ in/in/° F. in boththe Y and Z directions, and a CLTE in the range of 100 to 240° C. of1.16×10⁻⁵ in/in/° F. in the X direction and 3.4×10⁻⁵ in/in/° F. in boththe Y and Z directions. By contrast, PPS type polymer, (Fortron 4665)was likewise tested. While it had a low CLTE in the range of −30 to 30°C. (1.05×10⁻⁵ in/in/° F. in the X direction and 1.33×10⁻⁵ in/in/° F. inboth the Y and Z directions), it had a much higher CLTE in the range of100 to 240° C. (1.94×10⁻⁵ in/in/° F. in the X direction and 4.17×10⁻⁵in/in/° F. in both the Y and Z directions).

In addition to having a desirable CLTE, the preferred phase changematerial will also have a high thermal conductivity. A preferredthermoplastic material will have a thermal conductivity of at least 0.7watts/meter° K. using ASTM test procedure 0149 and tested at roomtemperature (23° C.).

Hard disc drives with a body of phase change material substantiallyencapsulating the stator 204, the actuator assembly housing 310 and thebase plate 108 wherein the phase change material has the CLTE or thermalconductivity as described above are themselves novel and define anotheraspect of the present invention. Once encapsulated, the hard disc drivewill preferably be able to meet disc drive manufacturers' industrystandards for extractable particles. Using laser particle counting, acumulative average of particles greater than 0.5 micrometers in sizewill total less than ten thousand particles per milliliter. This isprimarily because machined mounting plates are eliminated and othersources of particulates (steel laminations, wound wire and wire/terminalconnections) are sealed in the encapsulation.

Also, the encapsulation reduces outgassing because varnish used toinsulate wire in the windings and epoxy used to prevent steellaminations from oxidizing are hermetically sealed inside the statorassembly. Also, with fewer parts there is less glue needed to hold partstogether. This reduced outgassing reduces the amount of material thatcould affect the magnetic media or heads used in the disc drive.

Another aspect of the invention utilizes the basic motor described abovethat has dampened vibrations to make a hard disc drive. The dampenedvibrations can be either in the audible frequency range, thus resultingin a disc drive with less audible noise, or in other frequencies. Asmentioned earlier, the degree to which data can be packed onto a harddrive is dependent on how close the data tracks are spaced. Due toreduced vibrations resulting from aspects of the present invention, thedata tracks can be more closely spaced and the hard drive stilloperated.

The vibrations of concern are generally produced by harmonicoscillations. The phase change material can be selected so as to dampenoscillations at the harmonic frequency generated by operation of themotor, many of which are dependent on the configuration of the windingsor other conductors. Thus, in one aspect, the invention is a motor anddisc assembly wherein the motor comprises a stator having multipleconductors that create a plurality of magnetic fields when electricalcurrent is conducted through the conductors and a monolithic body ofphase change material substantially encapsulating the conductors. Inthis respect, the phase change material has a vibration dampening effectso that the motor and disc assembly has a reduction of harmonicoscillations.

There are a number of properties of the phase change material that canbe varied in a way that will allow the phase change material to dampendifferent harmonic frequencies. This includes adding or varying theamount of glass, Kevlar, carbon or other fibers in the material; addingor varying the amount of ceramic filler in the material; changing thetype of material, such as from polyphenyl sulfide to nylon or otherliquid crystal polymers or aromatic polyesters, adding or graftingelastomers into a polymer used as the phase change material; and using adifferent molecular weight when the phase change material is a polymer.Any change that affects the flex modulus, elongation or surface hardnessproperties of the phase change material will also affect its vibrationdampening characteristics.

One way to determine the effectiveness of vibration dampening, and thusto select a suitable material, is to make up motor configurations wheredifferent phase change materials are used, and then measure thevibration dampening accomplished by each material. The vibrationdampening can be measured with a capacitance probe or laser Dopplervibrometer. In the audible range, 20-15,000 Hz, the dampening willpreferably be at least 2, more preferably at least 5 decibels inreduction in harmonic frequency amplitude. These reductions are assessedbased on a comparison of the vibrations of the same motor but withoutthe stator being encapsulated.

The reduced vibrations thus allow for a unique hard disc drive with highdata density and method of manufacturing the same. In this aspect of theinvention, a hard disc drive is constructed with reduced vibrationcharacteristics. The disc drive includes a stator assembly and anactuator assembly housing that are encapsulated with the base plate toform a unitized structure with good structural properties. The reducedvibration characteristic of the hard drive is taken advantage of byhaving close data tracks on the magnetic storage media. Preferably thedata tracks are spaced so as to have at least 10,000 tracks/inch.

The vibration dampening ability of the phase change material may also beused in another aspect of the invention, a miniature hard disc drivehaving a high speed spindle motor with improved shock resistance. Inthis aspect of the invention, the body of phase change material is shockabsorbing and thus minimizes the transfer of energy between the housingof a hard disc drive and the magnetic storage media.

Also, with reduced vibration, there will be less friction and wear inthe bearings, which results in less heat being generated by the motor,in turn resulting in longer motor and bearing life and more power fromthe motor. Utilizing aspects of the present invention it is possible toconstruct motors able to spin in hard disc drives at speeds over 5,000rpm. A preferred motor will be able to spin at 7,500 rpm or greater, anda more preferred embodiment will be able to spin at 10,000 rpm orgreater.

A number of ways to improve thermal conductivity are presented. First,the phase change material will itself provide some heat dissipation.Second, the phase change material can include additives that willenhance its thermal conductivity. Third, the body of phase changematerial, by being in contact with a number of parts of the motor and/ordisc drive, can act as a pathway for heat such that those other parts ofthe motor and/or disc drive can act as heat sinks. This improved thermalconductivity provides longer life to the electrical and bearingcomponents of the motor, a higher power device, higher efficiency andlower current draw. If the motor is in a battery-powered device, thiswill extend the battery life.

Miniature hard disc drives built with the technique disclosed above willhave better reliability from lower particulate levels and reducedoutgassing. The hard drives will have improved shock resistance if thedrive is dropped. The preferred motors and disc drives will have quieteroperation.

The use of an encapsulated stator allows the terminal connectors 350 tobe integrated into the body, as shown in FIGS. 3, 5 and 6. In general,the motor can be more easily assembled and will include fewer parts. Asnoted above, the stack-up tolerances are reduced because fewercomponents are used and the phase change material can be designed with aCLTE that closely approximates that of other motor components.

It is contemplated that numerous modifications may be made to theminiature hard disc drive and method for making the miniature hard discdrive of the present invention without departing from the spirit andscope of the invention as defined in the claims. For example, while theexemplary embodiment shown in the drawings has a body 250 thatencapsulates the entire exposed top surface of base plate 108, it isconceivable that the body only encapsulates a portion of the top surfaceof the base plate so that the stator 204 and actuator assembly housing310 are unitized to the base plate 108. Furthermore, body 250 may alsoencapsulate connector pins that are inserted through the base plate 108without departing from the scope of the invention. Accordingly, whilethe present invention has been described herein in relation to severalembodiments, the foregoing disclosure is not intended or to be construedto limit the present invention or otherwise to exclude any such otherembodiments, arrangements, variations, or modifications and equivalentarrangements. Rather, the present invention is limited only by theclaims appended hereto and the equivalents thereof.

1. A disk drive, comprising: a molded enclosure including a base, acover, and a coupling mechanism to couple the base to the cover; a pivotinsert molded into the base; a spindle motor including a first portionand a second portion, the first portion of the spindle motor insertmolded into the base, the second portion of the spindle motor attachedto the first portion to form the spindle motor; a disk mounted to thespindle motor; and a head stack assembly having a coil portion pivotallycoupled to the pivot.
 2. The disk drive of claim 1, further comprising abase voice coil motor plate insert molded into the base.
 3. The diskdrive of claim 2, further comprising a cover voice coil motor plateinsert molded into the cover, wherein, when the cover is coupled to thebase, the coil portion of the head stack assembly is disposed betweenthe cover voice coil motor plate and the base voice coil motor plate. 4.The disk drive of claim 1, wherein, the pivot is a pivot shaft that isinsert molded into the base and the head stack assembly is pivotallycoupled to the pivot shaft.
 5. The disk drive of claim 1, wherein, thepivot is a pivot receptacle that is insert molded into the base, thepivot receptacle to receive a centering pin of the head stack assemblysuch that when the centering pin is coupled to the pivot receptacle thehead stack assembly is pivotally coupled to the base.
 6. The disk driveof claim 1, wherein, the first portion of the spindle motor that isinsert molded into the base includes a mounting bracket, a stator, and abearing cartridge.
 7. The disk drive of claim 6, wherein, the secondportion of the spindle motor attached to the first portion of thespindle motor to form the spindle motor includes a rotating hub and aspindle shaft.
 8. The disk drive of claim 1, further comprising a rampfor the head stack assembly molded into the base.
 9. The disk drive ofclaim 1, further comprising a crash stop for the head stack assemblymolded into the cover.
 10. The disk drive of claim 1, further comprisinga crash stop latch molded into the cover.
 11. The disk drive of claim 1,wherein, the coupling mechanism includes a hinge.
 12. The disk drive ofclaim 11, wherein, the base, the cover, and the hinge of the moldedenclosure are molded together to form a single-piece enclosure.
 13. Thedisk drive of claim 11, wherein, the base, the cover, and the hinge ofthe molded enclosure are injection molded together.
 14. The disk driveof claim 1, wherein the molded enclosure is formed of a plasticmaterial.
 15. The disk drive of claim 14, wherein the plastic materialincludes a non-plastic filler.
 16. The disk drive of claim 15, whereinthe non-plastic filler includes a metallic material.
 17. The disk driveof claim 1, wherein at least a portion of the base includes a metal. 18.A disk drive, comprising: a molded enclosure including a base, a cover,and a coupling mechanism to couple the base to the cover, the baseincluding an insert molded mounting skeleton; a pivot attached to themounting skeleton; a spindle motor including a first portion and asecond portion, the first portion of the spindle motor attached to themounting skeleton, the second portion of the spindle motor mounted tothe first portion to form the spindle motor; a disk mounted to thespindle motor; and a head stack assembly having a coil portion pivotallycoupled to the pivot.
 19. The disk drive of claim 18, further comprisinga base voice coil motor plate attached to the mounting skeleton.
 20. Thedisk drive of claim 19, further comprising a cover voice coil motorplate insert molded into the cover, wherein, when the cover is coupledto the base, the coil portion of the head stack assembly is disposedbetween the cover voice coil motor plate and the base voice coil motorplate.
 21. The disk drive of claim 18, wherein, the pivot is a pivotshaft that is attached to the mounting skeleton and the head stackassembly is pivotally coupled to the pivot shaft.
 22. The disk drive ofclaim 18, wherein, the pivot is a pivot receptacle that is attached tothe mounting skeleton, the pivot receptacle to receive a centering pinof the head stack assembly such that when the centering pin is coupledto the pivot receptacle the head stack assembly is pivotally coupled tothe base.
 23. The disk drive of claim 18, wherein, the first portion ofthe spindle motor that is attached to the mounting skeleton includes amounting bracket, a stator, and a bearing cartridge.
 24. The disk driveof claim 23, wherein, the second portion of the spindle motor mounted tothe first portion of the spindle motor to form the spindle motorincludes a rotating hub and a spindle shaft.
 25. The disk drive of claim18, further comprising a ramp for the head stack assembly molded intothe base.
 26. The disk drive of claim 18, further comprising a crashstop for the head stack assembly molded into the cover.
 27. The diskdrive of claim 18, further comprising a crash stop latch molded into thecover.
 28. The disk drive of claim 18, wherein, the coupling mechanismincludes a hinge.
 29. The disk drive of claim 28, wherein, the base, thecover, and the hinge of the molded enclosure are molded together to forma single-piece enclosure, the base being molded around the mountingskeleton.
 30. The disk drive of claim 28, wherein, the base, the cover,and the hinge of the molded enclosure are injection molded together, thebase being injected molded around the mounting skeleton.
 31. The diskdrive of claim 18, wherein, the molded enclosure is formed of a plasticmaterial.
 32. The disk drive of claim 31, wherein, the plastic materialincludes a non-plastic filler.
 33. The disk drive of claim 18, wherein,the mounting skeleton includes a metallic material.
 34. The disk driveof claim 18, wherein, the mounting skeleton is metal.